How does your body digest a cigarette?

Everybody knows now that smoking is bad for you. But that wasn't always the case. In the 1940s, '50s and '60s, Americans smoked with reckless abandon -- in their offices, in department stores, on elevators, planes and buses. In 1965, nearly half of all Americans smoked. The World Health Organization officially took a stance against smoking in the 1970s, and rates have dropped steadily ever since -- now down to 21 percent [source: AHA]. In today's society, it would be unthinkable for someone to light up at his or her office desk or in an elevator. Just try it and see what happens.

Cigarette manufacturers were forced to list the ingredients in cigarettes in 1998, so the public is now aware that there are more than 4,000 chemicals in each and every smoke. Here's a list of the 10 most dangerous:

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Ammonia -- used to increase the absorption rate of nicotine. It's also used to clean your toilet, helps to treat wastewater (poop and pee) and is a key ingredient in liquid fertilizer.

Arsenic -- used as a pesticide on tobacco plants, it remains in the resulting cigarette. If you have a rat problem in your home, you can use arsenic to kill them.

Cadmium -- a metallic compound that tobacco collects from acidic soil. Is the battery in your cell phone low? Use cadmium to recharge it!

Formaldehyde -- a byproduct of cigarette smoke, this colorless gas is commonly used to preserve dead bodies for burial.

Acetone -- another byproduct from burning a cigarette. It's also found in nail polish remover and, like ammonia, is used to clean toilets.

Butane -- this byproduct is also used to help you light your cigarette, in the form of lighter fluid.

Propylene Glycol -- added to cigarettes to keep tobacco from drying out. What it really does is speed up the delivery of nicotine to the brain.

Turpentine -- used to flavor menthol cigarettes. This oil also can be used to thin paint and strip varnish from wood.

Benzene -- another byproduct from burning a cigarette. You can find benzene in pesticides and gasoline.

Lead and Nickel -- Yes, these are metals. Need we say more?

So how does your body digest these things? It really doesn't -- which is the problem with cigarettes.